1. Technical Field of the Invention
The present invention relates generally to an electrically-powered steering device which may be employed in automotive vehicles.
2. Background Art
Japanese Patent First Publication No. 8-164861 discloses a conventional electrically-powered steering device which consists of an electric motor linked to a steering shaft through a torque transmission mechanism, a torque detector measuring torque added to the steering shaft, and a motor controller controlling an output of the motor as a function of the measured torque. The motor, the torque detector, and the motor controller are installed integrally on a steering column.
The above steering device, however, has the drawback in that the motor, the torque detector, and the motor controller are placed around the steering shaft from different directions and assembled as a unit, therefore, the assembling is quite inconvenient. Particularly, orientations of electric terminals joined to the control substrate are different, thus resulting in complicated joints between the terminals and the control substrate and increase in manufacturing cost.
It is therefore a principal object of the invention to avoid the disadvantages of the prior art.
It is another object of the invention to provide an improved structure of an electrically-powered steering device which is easy of assembly and electrical connections between electric parts of the steering device and a control substrate.
According to one aspect of the invention, there is provided an electrically-powered steering device which comprises: (a) a motor working to produce torque for assisting an operator in turning a steering wheel; (b) a torque transmission mechanism working to transmit the torque outputted by the motor to a steering shaft linked to the steering wheel; (c) a torque detector working to measure torque acting on the steering shaft; and (d) a controller working to control an output of the motor as a function of the torque measured by the torque detector. The motor, the torque transmission mechanism, the torque detector, and the controller are arranged integrally as a unit. The controller includes a motor driver which controls an exciting current supplied to the motor and a control substrate to which terminals of the motor driver are connected electrically, the control substrate being installed so that the steering shaft passes through a portion of the control substrate. The power terminals of the motor, terminals of the torque detector, and terminals of the motor driver extend in an axial direction of the steering shaft and connect electrically to the control substrate from the same side.
The steering shaft, as described above, passes through the control substrate. Specifically, the control substrate traverses the steering shaft. This provides for ease of the electrical connections of all the terminals to the control substrate.
In the preferred mode of the invention, the motor, the torque transmission mechanism, the torque detector, and the controller are constructed coaxially with the steering shaft, thereby allowing the steering device to have a compact structure as a whole, thus resulting in improved mountability of the steering device on vehicles.
The torque transmission mechanism may be implemented by a speed reduction gear mechanism using one of a worm gear and a hypoid gear which works to increase the torque outputted by the motor and transmit it to the steering shaft, thereby permitting the size of the motor to be decreased.
The torque transmission mechanism may also be implemented by one of a planetary gear speed reduction mechanism and a wave gear speed reduction mechanism, thereby permitting the torque transmission mechanism to be constructed as a whole coaxially with the steering shaft.
The torque detector is made up of a magnet and a magnetic sensor.
The torque detector is disposed in close proximity to a periphery of the steering shaft. Specifically, the torque detector is located apart from an external magnetic field, thus minimizing an error in operation thereof caused by the magnetic field.